OBJECTIVES: To measure the adherence to antibiotic treatment guidelines distributed to physicians in Washington State, USA. The Washington Department of Health, Washington State Medical Association (WSMA) and Health Plans understand that antibiotic resistance is a current problem and by distributing these guidelines they hope to decrease or stop the increase in development of resistance to currently available antibiotics. METHODS: Strong Square, LLC has developed an integrated database of medical, pharmacy and professional claims from seven participating health plans in Washington state for the purposes of measuring the impact the previously distributed antibiotic prescribing guidelines. Guideline adherence measurements included: 1) antibiotic prescribing rates by diagnosis; and 2) antibiotic drug formulary compliance. Diagnoses included in the data set are: Acute Otitis Media (AOM), Acute Pharyngitis (AP), Acute Uncomplicated Sinusitis (AUS), Community Acquired Pneumonia (CAP) and Uncomplicated Acute Bronchitis (UAB). The participating health plans, which include fee-for-service, HMO, managed care and state funded Medicaid programs, represent 87% of Washington state's population, 7,524 licensed primary care prescribers and 220,641 outpatient antibiotic treatment episodes from January 1, 2000 through September 30, 2002. RESULTS: The percentage of antibiotic diagnoses with antibiotic prescribing varied among the different types of respiratory tract infections. Prescribing rates are as follows: AOM, 48.4%; AP, 39.7%; AUS, 62.3%; CAP 48.7%; UAB, 54.3%. When antibiotic drugs were used, formulary compliance was also measured: AOM, 84.0%; AP, 53.3%; AUS, 68.1%; CAP 60.3%; UAB, 54.6%. CONCLUSIONS: Providing prescribers feedback measures for the guidelines they are expected to follow is a logical step towards improving rates of guideline adherence. Integrated reporting of diagnosis and drug data over a broad geographic region allows us to provide comprehensive, interpretive feedback to prescribers regarding their antibiotic prescribing patterns.